This should be because of the high temperature in the heating room, the high moisture content in the air and the low temperature downstairs. Obviously, the balcony is not insulated, so the cold balcony floor will produce a lot of condensed water, plus there is no water, so it will be cloudy.
It is suggested to add a commonly used foam insulation layer and then make a cement surface layer. If it is safer, you can also make a layer of water before making bricks.